During operation of such a vortex flowmeter, a Karman vortex street is formed downstream of the bluff body. Its pressure fluctuations are converted by a vortex-sensing element into an electric signal whose frequency is proportional to the volumetric flow rate.
The turbulence grid, which is mounted upstream of the bluff body, generates miniature vortices which contribute to a uniformity of the flow profile. Turbulence grids are not to be confused with flow conditioners, see U.S. Pat. No. 3,965,730, with flow straighteners or flow rectifiers, see U.S. Pat. No. 4,280,360 or U.S. Pat. No. 5,193,399.
Whereas flow straighteners dampen or even suppress turbulences of the flow, i.e. laminarize the flow, turbulence grids generate particularly well-defined turbulences. Flow rectifiers are also used together with turbulence grids upstream or downstream of the latter to increase the measurement accuracy.
U.S. Pat. No. 4,397,192 describes a vortex flow sensor for measuring the flow velocity and/or the volumetric flow rate of a fluid flowing in a measuring tube, comprising:
a bluff body (therein named "vortex-shedding obstacle") mounted in the measuring tube and designed to generate Karman vortices; PA1 a vortex-sensing element responsive to vortex-induced pressure fluctuations; and PA1 a turbulence grid mounted upstream of the bluff body and having openings with identical, square cross sections. PA1 a bluff body mounted in the measuring tube and designed to generate Karman vortices; PA1 a vortex-sensing element responsive to vortex-induced pressure fluctuations; and PA1 a turbulence grid mounted upstream of the bluff body and having openings with at least partially differing cross sections. PA1 20D&lt;x&lt;40D.